This application is based on Japanese Patent Application No. 11-367990 filed Dec. 24, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a braking pressure control apparatus including a diagnosing device.
2. Discussion of Related Art
JP-A-10-100884 discloses an example of a braking pressure control apparatus including a diagnosing device. The braking pressure control apparatus disclosed in this publication includes (1) a first hydraulic system including a first hydraulic pressure source which is power-operated to pressurize a working fluid and capable of controlling a pressure of the pressurized fluid, for operating a brake with the pressurized fluid delivered from the first hydraulic pressure source, (2) a second hydraulic system including a second hydraulic pressure source in the form of a master cylinder which is operable by an operating force acting on a manually operated brake operating member, to pressurize the working fluid to a pressure corresponding to the operating force, for operating the brake with the pressurized fluid delivered from the master cylinder, (3) a switching device for selectively establishing a first state in which the brake is operated with the pressurized fluid delivered from the first hydraulic pressure source, and a second state in which the brake is operated with the pressurized fluid delivered from the second hydraulic pressure source, and (4) a diagnosing device operable to diagnose the second hydraulic system for any abnormality on the basis of the pressure of the fluid in the master cylinder and the pressure of the fluid in the brake.
In the braking pressure control apparatus disclosed in the publication identified above, the second hydraulic pressure source is adapted to deliver the pressurized fluid on the basis of the operating force of the brake operating member, but the pressure of the pressurized fluid delivered from the second hydraulic pressure source is not higher than a level corresponding to the operating force of the brake operating member. Therefore, the diagnosing device used in this conventional braking pressure control apparatus may suffer from a drawback if the diagnosing device is used for a second hydraulic system which includes a second hydraulic pressure source adapted to deliver the working fluid to a pressure higher than a level corresponding to the operating force of the brake operating member.
It is an object of the present invention to provide a braking pressure control apparatus including a diagnosing device suitable for diagnosing a second hydraulic system which includes a second hydraulic pressure source adapted to pressurize the working fluid to a pressure higher than a level corresponding to the operating force of the brake operating member.
The above object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking pressure control apparatus for a hydraulically operated brake, comprising:
a first hydraulic system including a first hydraulic pressure-source which is power-operated to pressurize a working fluid and capable of controlling a pressure of the pressurized fluid, for operating the brake with the pressurized fluid delivered from the first hydraulic pressure source;
a second hydraulic system including a manually operable brake operating member, and a second hydraulic pressure source which is operable by an operating force acting on the brake operating member, to pressurize the working fluid to a pressure higher than a level corresponding to the operating force, for operating the brake with the pressurized fluid delivered from the second hydraulic pressure source;
a switching device operable to selectively establish a first state in which the brake is operated with the pressurized fluid delivered from the first hydraulic pressure source, and a second state in which the brake is operated with the pressurized fluid delivered from the second hydraulic pressure source; and
a diagnosing device operable to diagnose the second hydraulic system on the basis of a pressure of the fluid in the second hydraulic system.
In the braking pressure control apparatus according to the above mode (1) of this invention, the second hydraulic system provided to pressurize the fluid to a pressure level higher than a level corresponding to the operating force of the brake operating member can be diagnosed for any abnormality, by the diagnosing device on the basis of the fluid pressure in the second hydraulic system. As described in detail with respect to various specific forms or modes of this invention, the time required for diagnosing the second hydraulic system can be significantly reduced. In this respect, it is noted that a difference between the fluid pressure in the second hydraulic pressure source and the fluid pressure in the brake is generally larger than a difference between the fluid pressure in the master cylinder and the fluid pressure in the brake. If the second hydraulic system were diagnosed on the basis of the difference between the fluid pressure in the second hydraulic pressure source and the fluid pressure in the brake, as in the conventional braking pressure control apparatus wherein the second hydraulic system is diagnosed on the basis of the difference between the master cylinder pressure and the fluid pressure in the brake, it would take a longer time for the fluid pressure in the second hydraulic pressure source and the fluid pressure in the brake to become equal to each other. The present braking pressure control apparatus has a further advantage that a hydraulic booster included in the second hydraulic pressure source can be diagnosed. In the conventional braking pressure control apparatus, the hydraulic booster cannot be diagnosed.
The fluid pressure in the second hydraulic system on which the second hydraulic system is diagnosed may include a pressure of the fluid in the second hydraulic pressure source, a pressure of the fluid in a fluid passage connecting the second hydraulic pressure source and a cylinder for the brake, and a pressure in the brake during an operation of the brake with the pressurized fluid delivered from the second hydraulic pressure source.
Abnormalities of the second hydraulic system that can be detected by the diagnosing device include; abnormalities of elements of the second hydraulic system (e.g., an abnormality of the second hydraulic pressure source); and abnormalities of detectors provided to detect the operating states of the above-indicated elements (e.g., an abnormality of a pressure sensor for detecting the fluid pressure in the second hydraulic pressure source). Where the present braking pressure control apparatus is adapted to control the pressure of the fluid pressurized by the first hydraulic pressure source on the basis of the detectors indicated above, these detectors may be considered to be elements of the first hydraulic system. Since those detectors are used to detect the operating states of the elements of the second hydraulic system, however, the detectors are considered to be included in the second hydraulic system, in the present application.
In the above mode (1), the xe2x80x9clevel corresponding to the operating forcexe2x80x9d of the manually operable brake operating member is typically a pressure linearly proportional to the operating force of the brake operating member. However, the pressure level corresponding to the operating force need not be linearly proportional to the operating force, provided that the pressure level in question is determined depending upon the operating force. (2) A braking pressure control apparatus according to the above mode (1), wherein the diagnosing device diagnoses the second hydraulic system on the basis of the pressure of the fluid pressurized by the second hydraulic pressure source and a pressure of the fluid in the manually operable brake while the second state is established by the switching device.
In the braking pressure control apparatus according to the above mode (2), the diagnosis of the second hydraulic system is effected on the basis of the pressure of the fluid pressurized by the second hydraulic pressure source and the fluid pressure in the brake. In the second state, the second pressure source and the hydraulic cylinder of the brake are held in communication with each other, so that the fluid pressure in the brake must be substantially equal to the pressure of the fluid pressurized by the second hydraulic pressure source if the second hydraulic system is normal. When the absolute value of a difference between the pressure of the second hydraulic pressure source and the pressure of the brake is larger than a predetermined threshold, for instance, it indicates an abnormality of at least one of the pressure sensors provided to detect the pressures of the second hydraulic pressure source and the brake cylinder, or an abnormality of at least one of the second hydraulic pressure source, a fluid passage connecting the second hydraulic pressure source and the brake cylinder, and the brake cylinder.
In the braking pressure control apparatus according to the above mode (2), the second hydraulic system is diagnosed while the brake operating member is operated and while the second state is established by the switching device. Namely, the second hydraulic system is diagnosed at an opportunity other than an initial check of the apparatus prior to an operation of the brake. Thus, the number of opportunities at which the second hydraulic system is diagnosed is increased.
When a command to diagnose the second hydraulic system is generated while the brake is operated in the first state, the diagnosis is effected after the first state is switched to the second state. Where the brake is used to brake a wheel of a vehicle, the switching to the second state is preferably effected while the vehicle is stationary. The switching from the first state to the second state may cause a change in the braking force generated by the brake. This change does not give an adverse influence on the vehicle if the change takes place while the vehicle is stationary. In this case, the diagnosis is effected while the vehicle is stationary.
Where the diagnosis of the second hydraulic system is effected after the operating or control state of the apparatus is switched from the first state to the second state, it is desirable to first control the first hydraulic pressure source in the first state so that the fluid pressure in the brake is controlled to a level that is to be established when the second state is established, and then switch the operating state to the second state. This arrangement makes it possible to reduce the amount of change of the fluid pressure in the brake upon switching of the operating state from the first state to the second state. In this case, it is possible to rapidly increase the fluid pressure in the brake cylinder to a level close to the level of the second hydraulic pressure source. Accordingly, the time required for diagnosing the second hydraulic system is reduced. (3) A braking pressure control apparatus according to the above mode (2), wherein the diagnosing device includes a switching portion operable when the first state is established, to change the first state to the second state after the fluid pressure in the brake has been controlled in the first state to a level close to the fluid pressure in the second hydraulic pressure source.
(4) A braking pressure control apparatus according to the above mode (2) or (3), wherein the second hydraulic system comprises:
a first pressure sensing device for detecting the pressure of the fluid pressurized by the second hydraulic pressure source; and
a second pressure sensing device for detecting the pressure of the fluid in the brake,
and wherein the diagnosing device includes a sensor-diagnosing portion operable to diagnose at least one of the first and second pressure sensing devices, on the basis of the pressures detected by the first and second sensing devices.
The sensor-diagnosing portion of the diagnosing device provided according to the above mode (4) may be adapted to determine that at least one of the first and second pressure sensing devices is abnormal, if the absolute value of a difference between the fluid pressures of the brake and the second hydraulic pressure source which are detected by the respective first and second pressure sensing devices is larger than a predetermined threshold value.
(5) A braking pressure control apparatus according to the above mode (4), further comprising:
a first braking pressure control device operable while the first state is established by the switching device, to control the pressure of the fluid in the brake on the basis of the pressure of the fluid detected by the first pressure sensing device; and
a second braking pressure control device operable when the sensor-diagnosing portion determines that the first pressure sensing device is abnormal while the first state is established by the switching device, the second braking pressure control device controlling the pressure of the fluid in the brake on the basis of an operating amount of the manually operable brake operating member.
In the braking pressure control apparatus according to the above mode (5), the fluid pressure in the brake is controlled by the first braking pressure control device while the second hydraulic system is diagnosed to be normal. Since the pressure of the pressurized fluid corresponds to the operating force of the brake operating member, the fluid pressure in the brake can be controlled on the basis of the fluid pressure detected by the first pressure sensing device, such that the braking force generated by the brake is controlled as desired by the operator of an automotive vehicle where the present braking pressure control apparatus is used for braking the vehicle. For instance, the fluid pressure in the brake is controlled so that the detected actual braking force coincides with a desired value determined by the detected operating amount of the brake operating member.
Where the first hydraulic system includes a power-operated pressurizing device, and a pressure control valve device for controlling the pressure of the fluid pressurized by the pressurizing device, the fluid pressure in the hydraulically operated brake can be controlled by controlling the pressure control valve device. Where the first hydraulic system does not include a pressure control valve device as described above, the fluid-pressure in the brake can be controlled by controlling an amount of power to be supplied to the pressurizing device.
When the second pressure sensing device of the second hydraulic system is diagnosed to be abnormal, the fluid pressure in the brake is controlled by the second braking pressure control device, on the basis of the operating amount of the manually operable brake operating member. The operating amount may be the operating stroke or force of the brake operating member. By controlling the fluid pressure in the brake on the basis of the operating stroke or force of the brake operating member, the fluid pressure in the brake can be controlled so as to generate the braking force as desired by the vehicle operator, as in the case where the fluid pressure in the brake is controlled on the basis of the pressure of the fluid pressurized by the second hydraulic pressure source.
As described later in detail in the DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS, the fluid pressure in the brake may be controlled on the basis of the operating stroke of the brake operating member, the fluid pressure of the second hydraulic pressure source, and a predetermined weight of the operating stroke and the fluid pressure of the second hydraulic pressure source with respect to each other, while the second hydraulic system is normal, and on the basis of only the operating stroke of the brake operating member while the second hydraulic system is abnormal. In the later case, that is, where the second hydraulic system is abnormal, no weight is given on the fluid pressure of the second hydraulic pressure source, and the weight or ratio of the operating stroke with respect to the fluid pressure of the second hydraulic pressure source is equal to xe2x80x9c1xe2x80x9d.
(6) A braking pressure control apparatus according to any one of the above modes (1)-(5), wherein the second hydraulic system comprises:
a hydraulic booster including a power piston which is operatively connected to the manually operable brake operating member and which partially defines a booster chamber on a rear side of the power piston as viewed in a direction of an advancing movement of the power piston when the brake operating member is operated, the booster chamber being arranged to receive a pressurized fluid whose pressure corresponds to the operating force of the brake operating member; and
a booster pressure sensor for detecting the pressure of the pressurized fluid in the booster chamber,
and wherein the diagnosing device diagnoses the second hydraulic system on the basis of the pressure of the pressurized fluid in the booster chamber detected by the booster pressure sensor.
In the braking pressure control apparatus according to the above mode (6), the diagnosing device may be arranged to determine that the second hydraulic pressure source is abnormal, if the fluid pressure in the booster chamber of the hydraulic booster is lower than a predetermined threshold value (lower limit). In this case, it is considered that at least the hydraulic booster is not normally functioning. The threshold value used by the diagnosing device may be a value almost equal to the atmospheric pressure.
(7) A braking pressure control apparatus according to the above mode (6), wherein the second hydraulic system comprises:
a master cylinder including a pressurizing piston which is operatively connected to the power piston and which partially defines a pressurizing chamber on one of opposite sides thereof remote from the power piston; and
a master-cylinder pressure sensor for detecting a pressure of the fluid in the pressurizing chamber,
and wherein the diagnosing device diagnoses the second hydraulic system on the basis of the fluid pressure detected by the master-cylinder pressure sensor and the fluid pressure detected by the booster pressure sensor.
In the braking pressure control apparatus according to the above mode (7) wherein the fluid pressure in the pressurizing chamber of the master cylinder as well as the fluid pressure in the booster chamber of the hydraulic booster is used by the diagnosing device to diagnose the second hydraulic system, the second hydraulic system can be diagnosed with a higher decree of accuracy than when only the fluid pressure in the booster chamber is used for the diagnosis. Further, the present arrangement has an advantage of permitting a more detailed diagnosis of the second hydraulic system, for instance, a diagnosis as to whether the hydraulic booster or the master cylinder is abnormal.
The second hydraulic system is generally designed such that the fluid pressure in the master cylinder and the fluid pressure in the hydraulic booster are equal to each other. It is also noted that the fluid in the pressurizing chamber is pressurized to a level corresponding to a distance of the advancing movement of the pressurizing piston, so that it is possible to determine that the pressurizing piston has been advanced by only the operating force of the brake operating member, or by both the operating force of the brake operating member and an assisting force based on the fluid pressure in the booster chamber, if the fluid pressure in the pressurizing chamber of the master cylinder is higher than a predetermined threshold or lower limit. It is also possible to determine that the hydraulic booster is not normally functioning, if the fluid pressure in the booster chamber is lower than the predetermined threshold, as described above with respect to the above mode (6).
Therefore, the use of the fluid pressure in the master cylinder and the fluid pressure in the hydraulic booster improves the accuracy or reliability of diagnosis of the second hydraulic system by the diagnosing device, or permits the detailed diagnosis of the second hydraulic system. For instance, the diagnosing device may be arranged to determine that the second hydraulic system is normal, when the fluid pressures of the master cylinder and the hydraulic booster are equal to each other, and when these fluid pressures are both higher than the respective threshold values. Further, the diagnosing device may determine that the master cylinder and the hydraulic booster are both normal, when the conditions indicated above are satisfied. Other forms of diagnosis by the diagnosing device will be described with respect to the following modes (8) and (9).
(8) A braking pressure control apparatus according to the above mode, wherein the diagnosing device determines that the master cylinder is normal while the hydraulic booster is abnormal, when the pressure of the fluid in the pressurizing chamber detected by the master-cylinder pressure sensor is not lower than a predetermined threshold, while the pressure of the fluid in the booster chamber detected by the booster pressure sensor is lower than a predetermined threshold.
In the above conditions in which the pressure in the pressurizing chamber is not lower than the threshold while the pressure in the booster chamber is lower than the threshold, it is possible to determine that the fluid in the pressurizing chamber is pressurized as a result of an advancing movement of the pressurizing piston with the operating force of the brake operating member, but not as a result of the assisting force based on the fluid pressure in the booster chamber. In this case, it is possible to determine that the master cylinder is normal while the hydraulic booster is abnormal. It is desirable that the threshold for the fluid pressure in the pressurizing chamber be higher than the threshold for the fluid pressure in the booster chamber.
(9) A braking pressure control apparatus according to the above mode (7) or (8), wherein said hydraulic booster includes a pressure regulating portion which is connected to a high-pressure source capable of delivering a pressurized fluid whose pressure is higher than a maximum pressure of the fluid pressurized by the second hydraulic pressure source and which is operable to regulate the pressure of the pressurized fluid received from the high-pressure source to a level corresponding to the pressure of the fluid in the pressurizing chamber, the hydraulic booster having a fluid passage through which the pressurized fluid whose pressure has been regulated by the pressure regulating portion is supplied to the booster chamber,
and wherein the diagnosing device determines that the master cylinder is abnormal, when the fluid pressure in the pressurizing chamber detected by the master-cylinder pressure sensor is lower than a predetermined threshold while the fluid pressure in the booster chamber detected by the booster pressure sensor is lower than a predetermined threshold.
Where the fluid in the pressurizing chamber cannot be pressurized due to an abnormality of the master cylinder, the pressure of the pressurized fluid as regulated by the pressure regulating portion of the hydraulic booster is substantially equal to the atmospheric level, so that the pressure of the fluid in the booster chamber is also substantially equal to the atmospheric level. In this case, therefore, it is possible to determine that the master cylinder is abnormal. Abnormalities of the master cylinder include a sticking of the pressurizing piston at a certain position in the cylinder bore of the master cylinder due to a damage of the pressurizing piston and/or the cylinder bore.
The second hydraulic system may be diagnosed to be abnormal, when the fluid pressure in the pressurizing chamber of the master cylinder is lower than the fluid pressure in the booster chamber of the hydraulic booster, even if the fluid pressures in the pressurizing and booster chamber are both higher than the respective threshold values.
(10) A braking pressure control apparatus according to any one of the above modes (6)-(9), further comprising:
a first braking pressure control device operable while the first state is established by the switching device, to control the pressure of the fluid in the brake on the basis of the pressure of the fluid detected by the first pressure sensing device; and
a second braking pressure control device operable when the sensor-diagnosing portion determines that the first pressure sensing device is abnormal while the first state is established by the switching device, the second braking pressure control device controlling the pressure of the fluid in the brake on the basis of an operating amount of the manually operable brake operating member,
and wherein the second hydraulic system comprises:
a master cylinder including a pressurizing piston which is operatively connected to the power piston and which partially defines a pressurizng chamber on one of opposite sides thereof remote from the power piston; and
a master-cylinder pressure sensor for detecting a pressure of the fluid in the pressurizing chamber,
and wherein the first braking pressure control device includes a portion operable to control the pressure of the fluid in the brake on the basis of the pressure of the fluid in the pressurizing chamber detected by the master-cylinder pressure sensor.
The fluid in the pressurizing chamber of the master cylinder is pressurized to a level corresponding to the operating force of the brake operating member, so that the fluid pressure in the brake can be controlled to a level corresponding to the operating force of the brake operating member, by controlling the fluid pressure in the brake on the basis of the fluid pressure in the pressurizing chamber. Although the fluid pressure in the brake can be controlled to the level corresponding to the operating force of the brake operating member, on the basis of the fluid pressure in the booster chamber of the hydraulic booster, this control of the fluid pressure in the brake cannot be effected if the hydraulic booster is abnormal. In the braking pressure control apparatus according to the above mode (10) wherein the fluid pressure in the brake is controlled on the basis of the fluid pressure in the pressurizing chamber, the fluid pressure in the brake can be controlled to the level corresponding to the operating force of the brake operating member, even when the hydraulic booster is abnormal. Thus, the braking pressure control apparatus according to the above mode (10) assures an increased degree of reliability of control of the fluid pressure in the brake according to the brake operating force.
(11) A braking pressure control apparatus according to any one of the above modes (1)-(10), wherein the second hydraulic system comprises:
a pressure sensing device for detecting the pressure of the fluid pressurized by the second hydraulic pressure source; and
an operating amount sensing device for detecting an operating amount of the manually operated brake operating member,
and wherein the diagnosing device diagnoses the second hydraulic system on the basis of the pressure of the pressurized fluid detected by the pressure sensing device and the operating amount of the brake operating member detected by the operating amount sensing device.
The fluid is pressurized by the second hydraulic pressure source to a level corresponding to the operating amount of the brake operating member. That is, there is a predetermined ideal or normal relationship between the operating amount of the brake operating member and the pressure of the fluid pressurized by the second hydraulic pressure source. Accordingly, the second hydraulic system can be diagnosed on the basis of a relationship between the actually detected values of those two parameters as compared with the normal relationship.
In the braking pressure control apparatus according to the above mode (11), the diagnosing device is capable of diagnosing the second hydraulic system while either of the first state and the second state is established by the switching device. Usually, the relationship between the brake operating amount of and the fluid pressure of the second hydraulic pressure source in the first state is different from that in the second state. In either of these two states, however, the second hydraulic system can be diagnosed by determining whether there exists the predetermined ideal or normal relationship between the detected values of those two parameters.
Further, the cylinder of the brake can be diagnosed for the presence of air in the brake cylinder, on the basis of the relationship between the operating stroke (as the operating amount) of the brake operating member and the fluid pressure of the second hydraulic pressure source in the second state of the apparatus. A relatively low rate of increase of the fluid pressure in the brake cylinder with an increase of the brake operating stroke indicates the presence of air in the brake cylinder.
(12) A braking pressure control apparatus according to the above mode (11), wherein the second hydraulic system includes a plurality of brake cylinders for respective brakes, and fluid passages connecting the brake cylinders to the second hydraulic pressure source, the fluid passages including at least one main fluid passage connected to the second hydraulic pressure source, and at lest one connecting passage each of which is connected to one of the at least one main fluid passage and connects at least two of the plurality of brake cylinders to each other, the braking pressure control apparatus further comprising:
a communicating valve provided in at least one of the at least one connecting passage and is operable between an open state in which the at least two brake cylinders are held in communication with each other, and a closed state in which the at least two brake cylinders are disconnected from each other,
and wherein the diagnosing device diagnoses the at least two brake cylinders for the presence of air contained therein, on the basis of amounts of change of the operating stroke of the brake operating member and the pressure of the fluid pressurized by the second hydraulic pressure source while the communicating valve is placed in the open state and those while the communicating valve is placed in the closed state.
While the communicating valve is placed in the open state, the fluid pressurized by the second hydraulic pressure source is delivered to all of the at least two brake cylinders through the corresponding main fluid passage and connecting passage. While the communication valve is placed in the closed state, the fluid pressurized by the second hydraulic pressure source is not delivered to the brake cylinder or cylinders which is/are connected to the main fluid passage through the connecting passage. Based on these facts, each of the brake cylinders can be diagnosed for the presence of air contained therein, on the basis of the amounts of change of the brake operating stroke and the fluid pressure of the second hydraulic pressure source while the communicating valve is in the open state and those while the communication valve is in the closed sate.
For instance, the two brake cylinders are connected to the second hydraulic pressure source such that one of the brake cylinders is connected directly to the second hydraulic pressure source through the main fluid passage, while the other brake cylinder is connected to the second hydraulic pressure source through the connecting passage and the main fluid passage. In this instance, the fluid pressurized by the second hydraulic pressure source is delivered to only one of the two brake cylinders and not to the other brake cylinder while the communicating valve provided in the connecting passage is placed in the closed state. If the amount of change of the fluid pressure of the second hydraulic pressure source with respect to the brake operating amount is excessively small in the closed state of the communicating valve, it indicates that air is contained in the above-indicated one brake cylinder. If the amount of change of the fluid pressure of the second hydraulic pressure source is normal in the closed state of the communicating valve but is excessively small in the open state, it indicates that air is contained in the other brake cylinder.
(13) A braking pressure control apparatus according to any one of the above modes (1)-(12), wherein the second hydraulic system includes a high-pressure source capable of delivering a pressurized fluid whose pressure is higher than a maximum pressure of the fluid pressurized by the second hydraulic pressure source,
and wherein the diagnosing device diagnoses the second hydraulic system on the basis of the pressure of the pressurized fluid of the high-pressure source as well as the pressure of the fluid pressurized by the second hydraulic pressure source.
The accuracy of diagnosis of the second hydraulic pressure source can be improved when the diagnosis is based on the pressure of the pressurized fluid delivered from the high-pressure source and the pressure of the second hydraulic pressure source. When the pressure of the high-pressure source is lower than a predetermined threshold, the pressure of the fluid pressurized by the second hydraulic pressure source may be abnormally lower or the fluid may not be pressurized by the second hydraulic pressure source. When the pressure of the second hydraulic pressure source is excessively low while the pressure of the high-pressure source is in a normal range, it means that the second hydraulic pressure source is abnormal.
The high-pressure source of the second hydraulic system may be separate from a high-pressure source of the first hydraulic system. Alternatively, a single high-pressure source may be commonly used for the first and second hydraulic systems. In the latter case, the braking pressure control apparatus is simplified and small-sized.
(14) A braking pressure control apparatus for a hydraulically operated brake including a brake cylinder, comprising:
a first hydraulic system including a first hydraulic pressure source which is power-operated to pressurize a working fluid and capable of controlling a pressure of the pressurized fluid to be delivered to the brake cylinder for operating the brake with the pressurized fluid delivered from the first hydraulic pressure source;
a second hydraulic system including a manually operable brake operating member, and a second hydraulic pressure source which is operable by an operating force acting on the brake operating member, to pressurize the working fluid to a pressure corresponding to the operating force, so that the fluid pressurized by the second hydraulic pressure source is delivered to the brake cylinder for operating the brake;
a switching device operable to selectively establish a first state in which the brake cylinder is supplied with the pressurized fluid delivered from the first hydraulic pressure source, and a second state in which the brake is supplied with the pressurized fluid delivered from the second hydraulic pressure source;
a stroke simulator device including a stroke simulator connected to the second hydraulic pressure source, and a simulator shut-off valve having a closed state in which the stroke simulator is disconnected from the second hydraulic pressure source, and an open state in which the stroke simulator is in communication with the second hydraulic pressure source: and
a diagnosing device operable to diagnose the stroke simulator device on the basis of an amount of change of an operating stroke of the brake operating member and an amount of change of the pressure of the fluid pressurized by the second hydraulic pressure source.
There is a know ideal or normal relationship between the amount of change of the operating stroke of the brake operating member and the amount of change of the pressure of the fluid pressurized by the second hydraulic pressure source while the stroke simulator device is normal. By comparing a relationship between the detected actual amounts of change of those two parameters with the normal relationship, the stroke simulator device can be diagnosed for any abnormality.
Abnormalities of the stroke simulator device include a fluid leakage from the stroke simulator, and an abnormality of the simulator shut-off valve (sticking of a valve member in the open or closed state of the valve).
If the amount of change of the fluid pressure of the second hydraulic pressure source with respect to the amount of change of the brake operating stroke while the simulator shut-off valve is commanded to be placed in its closed state is abnormally small, it indicates that the simulator shut-off valve is abnormally kept in its open state due to sticking of its valve member.
If the amount of change of the fluid pressure of the second hydraulic pressure source with respect to the brake operating member while the simulator shut-off valve is commanded to be placed in its open state is abnormally large, it indicates that the simulator shut-off valve is abnormally kept in its closed state due to sticking of its valve member.
If the amount of change of the fluid pressure of the second hydraulic pressure source with respect to the brake operating member while the simulator shut-off valve is placed in its open state is extremely small, it indicates that the stroke simulator is suffering from a fluid leakage.
(15) A braking pressure control apparatus according to the above mode (14), wherein the diagnosing device diagnoses the stroke simulator device while the second state is established by the switching device.
The stroke simulator device can be diagnosed irrespective of whether the first or second state is established by the switching device. If the simulator shut-off valve is switched from the open state to the closed state while the first state is established, the brake operating stroke is reduced to a considerably small value, unexpectedly to the operator of the present apparatus (e.g., the operator of an automotive vehicle provided with the apparatus). In the second state, however, the switching of the simulator shut-off valve to the closed state will not cause a reduction of the brake operating stroke since the pressurized fluid is delivered from the second hydraulic pressure source to the brake cylinder.
The brake cylinder can be diagnosed for the presence of air contained therein, on the basis of the amounts of change of the brake operating stroke and the fluid pressure of the second hydraulic pressure source while the second state is established by the switching device. When the amount of change of the fluid pressure of the second hydraulic pressure source with respect to the brake operating stroke is abnormally small, however, it is not possible to determine whether the simulator shut-off valve is abnormally kept in its open state, or the brake cylinder contains air. In this case, a diagnosis is repeated in the same manner after the operating state of the apparatus is switched from the second state to the first state. This diagnosis makes it possible to determine whether the brake cylinder contains air or the simulator shut-off valve is abnormal.
(16) A braking pressure control apparatus according to the above mode (15), wherein the second hydraulic system includes a plurality of brake cylinders for respective brakes, and fluid passages connecting the brake cylinders to the second hydraulic pressure source, the fluid passages including at least one main fluid passage connected to the second hydraulic pressure source, and at lest one connecting passage each of which is connected to the main fluid passage and connects at least two of the plurality of brake cylinders to each other, the braking pressure control apparatus further comprising:
a communicating valve provided in at least one of the at least one connecting passage and is operable between an open state in which the at least two brake cylinders are held in communication with each other, and a closed state in which the at least two brake cylinders are disconnected from each other,
and wherein the diagnosing device diagnoses the stroke simulator device while the communicating valve is placed in the closed state.
The amount of the pressurized fluid to be delivered from the second hydraulic pressure source to the plurality of brake cylinders is smaller when the communicating valve is placed in the closed state than when the communicating valve is placed in the open state. Accordingly, the amount of change of the fluid pressure of the second hydraulic pressure source with respect to the amount of change of the brake operating stroke when the stroke simulator device is normal is larger when the communicating valve is placed in the closed state than in the open state. Accordingly, the determination as to whether the stroke simulator device is normal or not can be made with a higher degree of accuracy when the communicating device is placed in the closed state.
It is also noted that the operating state of the brake operating member while the stroke simulator device is diagnosed by the diagnosing device in the second state of the apparatus is more similar to the operating state when the communicating valve is placed in the closed state than when it is placed in the open state. That is, the second hydraulic pressure source is disconnected from the brake cylinders and are held in communication with the stroke simulator when the apparatus is in the first state. In the second state in which the stroke simulator device is diagnosed, the operating state of the brake operating member as felt by the operator of the apparatus is more similar to that in the first state when some of the brake cylinders are disconnected from the second hydraulic pressure source by the communicating valve, than when all of the brake cylinders are communicated with the second hydraulic pressure source.
(17) A braking pressure control apparatus according to any one of the above modes (14)-(16), wherein the diagnosing device has a releasing passage connected at one end thereof to a low-pressure source and at the other end thereof to a portion of the stroke simulator device which is between the simulator shut-off valve and the stroke simulator, the diagnosing device including a releasing valve provided in the releasing passage and having an open state in which the stroke simulator device is communicated at the portion thereof to the low-pressure source, and a closed state in which the stroke simulator device is disconnected at the portion thereof from the low-pressure source,
and wherein the diagnosing device diagnoses the stroke simulator device on the basis of the amount of changes of the operating stroke of the brake operating member and the pressure of the fluid pressurized by the second hydraulic pressure source while the releasing valve is placed in the open state.
While the simulator shut-off valve is in the closed state, the brake operating stroke will not be excessively large even when the releasing valve is in the open state. While the simulator shut-off valve is in the open state, however, the brake operating member may be excessively large when the releasing valve is in the open state.
Accordingly, the stroke simulator device can be accurately diagnosed by suitably controlling the simulator shut-off valve and the releasing valve, based on the phenomenon indicated above.
(18) A braking pressure control apparatus according to any one of the above modes (14)-(17), further comprising an alarming device operable to provide an alarm when the diagnosing device has determined that the stroke simulator device is abnormal.
While the apparatus is in the first state, the operating state of the brake is not necessarily influenced immediately after the stroke simulator device becomes abnormal. However, an abnormality of the stroke simulator device may cause an excessively large amount of increase or decrease of the operating stroke of the brake operating member. In this respect, the provision of the alarming device is desirable for informing the operator of the apparatus that the stroke simulator device has become abnormal.
(19) A braking pressure control apparatus according to any one of the above modes (1)-(18), further comprising a controller for controlling the switching device to selectively establish the first and second states, depending upon a result of a diagnosis by the diagnosing device.
Where the hydraulic booster or master cylinder of the second hydraulic system is diagnosed to be abnormal, for instance, the controller commands the switching device to establish the first state so that the brake is operated with the pressurized fluid delivered from the first hydraulic pressure source. When the diagnosis is effected in the first state, the first state is maintained. When the diagnosis is effected in the second state, the operating state of the apparatus is switched from the second state to the first state. In the first state, the braking force generated by the brake is not reduced due to the abnormality of the second hydraulic system.
Where any sensor used in the second hydraulic system is diagnosed to be abnormal, the controller may be adapted to command the switching device to establish the second state. The diagnosis effected in the first state usually uses the output of the sensor or sensors provided in the second hydraulic system. In this case, the operating state of the apparatus may be changed from the first state to the second state, only where there is/are not a sensor or sensors that can be substituted for the sensor or sensors which has/have been diagnosed to be abnormal, as described below with respect to the following mode (20). The first state is changed to the second state where a detected abnormality makes it difficult or impossible to control the fluid pressure in the brake as needed.
(20) A braking pressure control apparatus according to any one of the above modes (1)-(19), further comprising a first braking pressure control device operable while no abnormality is detected by the diagnosing device, for controlling the fluid pressure in the brake in a predetermined normal manner, and a second braking pressure control device operable while an abnormality associated with at least one of predetermined at least one sensor is detected by the diagnosing device, for controlling the fluid pressure in the brake in a manner different from the predetermined normal manner, without using an output of the above-indicated at least one of the predetermined at least one sensor.
The second hydraulic system may include a plurality of sensors or detectors at least one of which is used to control the fluid pressure in the brake in the first state. In this case, the apparatus may include a sensor or sensors that can be substituted for the above-indicated at least one sensor, when the latter is diagnosed to be abnormal. For instance, the output of a master-cylinder pressure sensor for detecting the pressure of the master cylinder of the second hydraulic pressure source is used to control the fluid pressure in the brake while the master-cylinder pressure sensor is normal. If this master-cylinder pressure sensor is found abnormal, the output of a stroke sensor for detecting the operating stroke of the brake operating member may be used for controlling the fluid pressure in the brake. In an alternative arrangement wherein the fluid pressure in the brake is controlled on the basis of the detected pressure of the master cylinder and the detected brake operating stroke, the control of the fluid pressure in the brake may be effected on the basis of only the detected brake operating stroke where the sensor for detecting the master cylinder pressure or the master cylinder per se is diagnosed to be abnormal. In another alternative arrangement, the control of the fluid pressure in the brake is effected on the basis of the detected fluid pressure of the master cylinder and the detected fluid pressure of the hydraulic booster. In this case, the control may be effected on the basis of only the detected master cylinder pressure where the sensor for detecting the pressure of the hydraulic booster or the hydraulic booster per se is diagnosed to be abnormal.
The xe2x80x9cabnormality associated with at least one of predetermined at least one sensorxe2x80x9d may be an abnormality of the sensor or sensors per se, or an abnormality of a device or devices whose operating state or physical quantity is detected by the sensor or sensors.
(21) A braking pressure control apparatus for a hydraulically operated brake, characterized by comprising:
a first hydraulic system including a first hydraulic pressure source which is power-operated to pressurize a working fluid and capable of controlling a pressure of the pressurized fluid, for operating the brake with the pressurized fluid delivered from the first hydraulic pressure source;
a second hydraulic system including a manually operable brake operating member, and a second hydraulic pressure source which is operable by an operating force acting on the brake operating member, to pressurize the working fluid to a pressure higher than a level corresponding to the operating force, for operating the brake with the pressurized fluid delivered from the second hydraulic pressure source;
a switching device operable to selectively establish a first state in which the brake is operated with the pressurized fluid delivered from the first hydraulic pressure source, and a second state in which the brake is operated with the pressurized fluid delivered from the second hydraulic pressure source; and
a diagnosing device operable to diagnose the second hydraulic system on the basis of an operating state of the second hydraulic system.
In the braking pressure control apparatus according to the above mode (21), the second hydraulic system is diagnosed on the basis of its operating state.
(22) A braking pressure control apparatus according to any one of the above modes (1)-(21), further comprising a device for restricting an amount of change of at least one of an operating state of the brake operating member and the fluid pressure in the brake when the operating state of the apparatus is switched by the switching device between the first and second states.
(23) A braking pressure control apparatus according to any one of the above modes (1)-(22), further comprising a device for reducing a difference between the fluid pressure in the brake and the pressure of the fluid pressurized by the second hydraulic pressure source, when the operating state of the apparatus is switched by the switching device between the first and second states.
(24) A braking pressure control apparatus according to any one of the above modes (1)-(23), further comprising a device for reducing an amount of flow of the fluid between the second hydraulic pressure source and the brake when the operating state of the apparatus is switched by the switching device between the first and second states.
(25) A braking pressure control apparatus according to any one of the above modes (1)-(24), further comprising a device for restricting a rate of change of the fluid pressure in the brake when the operating state of the apparatus is switched by the switching device between the first and second states.
(26) A braking pressure control apparatus according to any one of the above modes (1)-(25), wherein the switching device switches the operating state of the apparatus from the first state to the second state, when the brake operating member is not in operation.
(27) A braking pressure control apparatus according to any one of the above modes (1)-(26), further comprising a device for restricting a change in control characteristic of the fluid pressure in the brake, when the operating state of the apparatus is switched by the switching device between the first and second states.
(28) A braking pressure control apparatus according to the above mode (27), wherein the above-indicated device for restricting a change in control characteristic controls the fluid pressure in the brake to a level which is expected to be established when the operating state has been switched from one of the first and second states to the other state.
(29) A braking pressure control apparatus according to any one of the above modes (1)-(28), further comprising a device for restricting a change in the operating state of the brake operating member unexpectedly to the operator of the apparatus, when the operating state of the apparatus is switched by the switching device between the first and second states.
(30) A braking pressure control apparatus according to any one of the above modes (1)-(29), further comprising a device for controlling the fluid pressure in the brake in a manner different from a predetermined normal manner, when the operating state of the apparatus is switched by the switching device between the first and second states.
(31) A braking pressure control apparatus according to any one of the above modes (1)-(30), further comprising a device for initiating an operation of restricting a change of at least one of the operating state of the brake operating member and the fluid pressure in the brake, when a symptom indicating that the operating state of the apparatus is likely to be switched by the switching device between the first and second states.